Multiple dose medication dispensing method

ABSTRACT

A multi-use pen-shaped medication dispensing device made of a plastic material that is recyclable after the contents of the medication cartridge have been exhausted. The device is made of a minimal number of parts, which include a housing, a dial assembly, a generally cylindrical button assembly located within the proximal end of the dial assembly, an internally threaded nut, and an externally threaded leadscrew. The device is arranged so that the dial must be rotated to the zero dose position prior to setting a dose. The device includes a lockout mechanism that prevents the dial from being depressed during dosing. The device further includes a mechanism that limits the maximum dosage that can be dialed up and a mechanism that prevents the user from dialing up a dosage greater than that remaining in the cartridge.

This is a division of application Ser. No. 08/399,764, filed Mar. 7,1995 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates generally to medical dispensing devicesand, more particularly, to a recyclable dispensing device that permitsselectively measured dosages of a liquid to be dispensed.

Patients suffering from diseases such as diabetes must inject themselvesseveral times each day with an insulin solution. Since the volume ofinsulin solution to be injected varies from injection to injection, itis necessary for such patients to be able to measure a precise volume ofinsulin. Diabetics have conventionally used a syringe for injection ofinsulin. However, it is difficult to control the operation of thesyringe as well as the quantity of drug injected.

In order to permit a diabetic to measure and administer a more accurateand controlled dosage, injector pens have been developed which enable aparticular dosage to be accurately and conveniently measured. Generally,these pens are secured onto a cartridge having a particular quantity ofliquid medication sealed therein. The cartridge includes a plunger and amechanism for advancing the plunger in the cartridge in such a manner todispense the medication. Injector pens may be reusable or disposable. Inreusable pens, a user can change a spent cartridge and reset theleadscrew of the pen back to its initial position. In a disposable pen,the cartridge is permanently captured in the pen which is disposed ofafter the contents of the cartridge have been exhausted.

One such disposable pen that has functioned very adequately is disclosedin U.S. Pat. No. 5,295,976. Specifically, a dispensing device isdisclosed and includes an internally threaded collar and an externallythreaded plunger rod. In order to set a dosage of medication to bedelivered, the collar is rotated thereby causing displacement of thecollar toward the proximal end of the injection device. Rotation of thecollar causes the integral cap to become effectively displaced bothrotationally and axially toward the proximal end of the pen. As thisdisplacement occurs, the segment of the dose-indicating scale which isvisible through a window varies showing a linear increase in the numberto indicate an increase dosage of liquid to be dispensed. Once thedesired dosage is selected, a force is applied to the end of the capcausing a linear displacement of the cap, integral plunger rod, andpiston to dispense liquid from the container. The dispensingdisplacement of the plunger rod is halted by abutting contact betweenthe cap and a stop element.

In U.S. Pat. No. 5,308,340, another recyclable injection device isdisclosed. In particular, a plunger rod is received within the housingfor exerting a force on a piston closing a second end of the container.The plunger rod has a noncylindrical cross section with a first surfaceincluding threads and a second surface which can, optionally, include aseries of ratchet teeth. A collar is received within the housingadjacent the second end of the container for permanently retaining thecontainer of liquid within the housing. The plunger rod passes throughthe noncylindrical opening in the collar and is prevented from rotatingwith respect to the housing by the collar. A hollow cap envelopes theplunger rod opposite the container of liquid. The skirt of the hollowcap extends inside the housing. The cap includes a threaded interiorsurface which movably engages the plunger rod for calibrated adjustmentrelative thereto. A stop is provided within the housing, and a distalfacing surface is provided on the hollow cap for contacting the stopupon linear movement of the cap and plunger rod as a unit toward thecontainer to dispense liquid therefrom. In operation, the cap is rotatedin a counterclockwise direction causing the threads of the cap to travelalong the threaded portion of the rod. This rotation does not causedisplacement of the plunger rod with respect to the housing, but backsthe distal end of the proximal cap portion away from a stop shoulder onthe inside of the housing. When the cap has been positioned to thedesired dosage, pressure is applied to the end of the cap for causing itto move linearly toward the distal end of the housing until a shoulderdefined by a radially exposed portion of the distal end contacts a stop.

SUMMARY OF THE INVENTION

The present invention provides a medication injection device comprisinga housing, a dose setting mechanism within the housing, and a deliverymechanism within the housing for advancing a leadscrew. A liquidmedication product is housed in a variable volume cartridge within thehousing of the device. Upon actuation of the delivery mechanism, theleadscrew is advanced against a movable piston in the cartridge toadvance the piston thereby causing a preset quantity of medication to bedelivered out of the needle of the device.

In one embodiment, the device is made entirely out of a recyclableplastic material, except for the glass container, steel needle andlabel. The dose setting mechanism comprises a dial assembly including aclutching device for engaging and disengaging a generally cylindricalinternally threaded nut, which is threaded onto an externally threadedleadscrew. A dose is set by rotating the nut with respect to theleadscrew. The nut is rotated by rotating the dial. However, the nutmust be engaged with the dial so that rotating the dial also rotates thenut. The clutching device comprises a series of splines on the innercylindrical surface of the dial which axially engage correspondingsplines on the outer surface of the nut. The splines are engaged withone another by retracting the dial with respect to the nut after thedial has been rotated to its zero dose position.

The dial assembly includes a mechanism that prevents the user fromretracting the dial prior to rotating the dial to its zero doseposition. This mechanism comprises a finger formed in the housing thatrides within a groove formed at the distal end of the dial assembly asthe dial assembly is rotated. The dial cannot be pulled out in anyradial position other than the zero dose radial position due to theinterference formed between the finger and the walls of the groove. Inthe zero dose position, the housing finger rides up within a spline thatextends axially uninterrupted to enable the dial to be proximallyretracted with respect to the housing only when the dial is in its zerodose radial position.

The device includes a mechanism that limits the maximum dosage that canbe set. This mechanism comprises a helical groove formed in the housingand a pair of flexible fingers formed in the dial assembly. Uponrotating the dial to set a dose, the dial is retracted with respect tothe housing because the dial fingers ride up the internal housinggroove. Once the dial fingers reach the proximal end of the housinggroove, further rotation of the dial is prohibited, thereby indicatingto the user that the maximum dosage has been dialed.

The device further includes a mechanism for automatically locking outthe dial from an inadvertent injection after the dial has been retractedto set a dosage. This lockout mechanism comprises the above-mentionedfingers in the dial assembly that fall into the helical groove in thehousing upon retracting the dial with respect to the housing. Theinterference fit formed by the fingers in the groove prevents forwardmovement of the dial in the event of inadvertent pressure being appliedto the end of the dial. The lockout mechanism is released by a buttonassembly that is disposed within the proximal end of the dial assembly.The button assembly is sized and configured so that it must be depressedupon initiating an injection. Upon depressing the button assembly, itbottoms out against the dial, whereupon the dial moves forwardly so thatthe flexible fingers move past the groove in the housing.

One of the two flexible fingers of the dial assembly has an extensionwhich, when the button is pressed, is pushed radially out. This fingerfalls within a separate groove in the housing as the "end-of-dose" stopsurface of the dial engages the corresponding stop surface on thehousing, thereby producing an audible "click" indicating that the entiredosage has been injected. The housing further includes radially inwardlyextending tangs at the proximal end thereof which engage ratchet teethin the leadscrew to prevent the leadscrew from backing up in theproximal direction. These tangs are in constant engagement with theleadscrew, thereby preventing the leadscrew from rotating upon rotationof the nut.

The device also includes a mechanism which indicates to the user thatthere is an insufficient dosage remaining in the container ofmedication. This mechanism prevents the user from setting a dosagegreater than that available to be delivered. The insufficient doseremaining feature comprises a 350° helical thread on the innercylindrical surface of the nut and a raised finger forward at the end ofthe leadscrew where the external thread terminates. As the nut rotatesabout the leadscrew, the ledge formed by the termination of the helicalthread on the nut engages the finger, thereby positively preventingfurther rotation of the nut in that direction.

An advantage of the medication dispensing device of the presentinvention is that the dosing function is locked out until the dial hasbeen rotated to its zero dose position, thereby ensuring an accuratedosage.

Another advantage of the present invention is that the device is aninexpensive recyclable pen that is designed to allow a user to dose insingle unit increments, which are each displayed in a single unitdisplay.

Another advantage of the present invention is that the end-of-dose clickarrangement is adjacent the end-of-dose stop to provide increasedaccuracy of an end of dose.

Another advantage of the present invention is that the device includes adosage lockout mechanism that prevents an inadvertent delivery of adosage of medication.

A further advantage of the present invention is that the insufficientremaining dose mechanism comprises a radial stop which ensures that theuser cannot dial up a dosage greater than that remaining in thecartridge.

Yet another advantage of the present invention is that the device ismade of inexpensive materials and is nearly 100% recyclable after thecontents of the cartridge have been depleted.

The present invention, in one form thereof, comprises an apparatus foreffecting delivery of an injectable product. The apparatus comprises ahousing and a container secured to the housing and including a piston,an exit, and an injectable product between the piston and the exit. Adrive stem is disposed in the housing and is in engagement with thepiston. The length of axial movement of the drive stem with respect tothe housing between a pre-injection position and a post-injectionposition defines the stroke length of the drive stem. A manuallyadjustable dosage metering mechanism is disposed in the housing and ismovable between a zero dose position, wherein the stroke length is zero,and a second dose position for enabling a user to selectively adjust thestroke length of the drive stem. The apparatus further includes meanscoupled to the dosage metering mechanism for preventing the strokelength of the drive stem from being adjusted until the dosage meteringmechanism has been set to the zero dose position.

In another form of the present invention, the apparatus includes a driveassembly mounted to the housing and manually advanceable in the housingbetween a dose setting position and an injection position for manuallymoving the drive stem to drive the piston within a container. The driveassembly is locked from movement with respect to the housing along theaxis of ejection while in the dose setting position. A disengagingdevice is secured to at least one of the drive assembly and the housingto unlock the drive assembly from the housing to enable the driveassembly to be axially advanceable with respect to the housing to movethe drive assembly from the dose setting position to the injectionposition.

The present invention further includes a method of delivering a selecteddosage of injectable product. The method includes the step of rotating aknob extending from an injector housing to establish a zero doserotational position of the knob, wherein rotation of the knob causesrotation of the dial assembly attached to the knob. The knob and dialassembly are retracted while in the zero dose position to cause the dialassembly to engage an internally threaded nut with the housing. The knobis then rotated to cause rotation of the dial and the nut which causesaxial translation of the dial and the nut, thereby setting a desireddosage of injectable product to be delivered. The knob is then manuallydepressed to depress the dial assembly and the nut and drive stem tocause the drive stem to advance the piston within the container ofinjectable product, thereby forcing a set dosage of injectable productto be delivered out of the exit of the container. The step of depressingthe knob causes the dial assembly to become disengaged from the nut sothat the knob may be rotated independently of the nut after delivery ofthe set dosage of injectable product has been completed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a medicationdispensing device in accordance with the present invention;

FIG. 2 is an exploded view of the device of FIG. 1;

FIG. 3 is an enlarged longitudinal sectional view of a portion of themedication dispensing device of FIG. 1, particularly showing the buttonassembly disposed within dial assembly;

FIG. 4 is an enlarged perspective view, in partial section, of themedication dispensing device of FIG. 1, particularly showing the buttonassembly disposed in the dial assembly;

FIG. 5 is an enlarged cross sectional view of the medication dispensingdevice of FIG. 1, particularly showing the insufficient remaining dosestop on the nut approaching the corresponding stop on the leadscrew;

FIG. 6 is a view of FIG. 5, except that the insufficient remaining dosestop on the nut is in engagement with the stop on the leadscrew;

FIG. 7 is a perspective view, in partial section, of a housing part inengagement with the dial assembly, particularly showing the unit clickfinger in the zero position;

FIG. 8 is a view of FIG. 7, except that the unit click finger is behindthe end-of-dose flange;

FIG. 9 is a view of FIG. 7, except that the unit click finger is shownin the dial splines during dosing;

FIG. 10 is an enlarged sectional view of a portion of the medicationdispensing device of FIG. 1, particularly showing the relationship amongthe button assembly, dial assembly, and housing while the device is atthe end of dose position;

FIG. 11 is a longitudinal sectional view of the medication dispensingdevice of FIG. 1, particularly showing the dial assembly after it hasbeen rotated to the zero position;

FIG. 12 is a view of FIG. 11 except that the dial assembly has beenretracted so that the splines of the nut are engaged by the splines ofthe dial assembly;

FIG. 13 is a view of FIG. 12, except that a desired dosage has beendialed up;

FIG. 14 is a view similar to FIG. 10, showing the dial assembly rotated180°, and further showing the button initially depressed before dialmovement takes place;

FIG. 15 is a view of FIG. 14, showing the dial having moved forward asmall distance;

FIG. 16 is a view of FIG. 14, showing the dial having moved forward halfof a thread pitch; and

FIG. 17 is a view of FIG. 13, except that the pen is shown in itsend-of-dose position.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For purposes of this application, the term "proximal" shall designate arelative axial position toward the knob end of the delivery mechanism,and the term "distal" shall designate a relative axial position towardthe delivery needle end of the delivery mechanism.

Referring to FIGS. 1 and 2, there is shown an injection medicationdevice 20 having the general appearance of a pen or mechanical pencil.The device comprises a mechanism housing 22 having a first part 24 and asecond part 26 (FIG. 2). Housing parts 24 and 26 are secured together ina suitable fashion, e.g. chemical bonding with a suitable adhesive or asolvent. A cap 28 is snapped onto the distal end of mechanism housing22. Cap 28 includes a clip 30 which cooperates with the side wall of cap28 to provide a convenient means for holding the pen device 20 in ashirt pocket. Referring to FIG. 2, the major components of medicationdevice 20 include a button assembly 32, a dial assembly 34, a nut 36,and a drive stem 38. A cartridge 40 is inserted into a distal body 42 towhich is attached a needle assembly 44 and needle cover 46. All of thecomponents of medication device 20, except cartridge 40 and needle 44may be made of a plastic material that is suitable for recycling.Suitable plastics are high flow polycarbonates resins which can beprocessed by conventional injection molding and extrusion. In oneembodiment, the housing parts 24, 26 and distal body 42 are made from anoptically clear polycarbonate material, and the remaining plasticcomponents are made from ABS resins. These plastics are recyclable,thereby making disposal of the device environmentally desirable.

Referring to FIG. 4, button assembly 32 comprises a hollow cylindricalportion 48 having a proximal end 50. Cylindrical portion 48 includes adistal end 52 in the form of an annular bead and further includes anenlarged diameter ring 54 comprising a tapered surface 56 and anenlarged diameter flat surface 58. The inner section of surfaces 56 and58 forms an enlarged diameter shoulder surface 60. The proximal end 50of button assembly 32 comprises two flexible fingers 62, 64, eachextending from a base surface 66. As shown in FIG. 4, each finger 62, 64is L-shaped and includes a first leg which extends from base surface 66and is parallel with the axis of medical device 20, and a second legextending radially about 90° from the first leg. Proximal end 50 ofbutton assembly 32 further includes a finger-engageable end 68 having arecessed surface 70. End 68 is integrally connected to hollowcylindrical portion 48 by connection portions 72 (FIG. 3). Proximal end50 includes a surface 74 (FIG. 3) that is formed from reduced lengthportion 76.

Referring to FIGS. 3 and 10, dial assembly 34 is shown in detail. Dialassembly 34 is generally cylindrical in shape and is hollow throughoutits axial length. The diameter of dial assembly 34 is at a maximum atits proximal end and is at a minimum at its distal end. Referring toFIG. 3, dial assembly 34 comprises a proximal knob portion 78, anintermediate portion 80, and a distal portion 82. Proximal knob portion78 comprises an enlarged diameter portion 84, a tapered portion 86, andan end-of-dose ring 91 extending about the circumference of proximalknob portion 78 as shown in FIG. 3. Ring 91 includes a bottom surface 89(FIG. 13) that constitutes a stop surface when engaged with the rear ofthe housing. Ring 91 also includes an enlarged "zero-dose" protrusion88. A generally U-shaped groove 90 (FIGS. 2, 3) is formed in proximalportion 78 to form a flexible section 92. The proximal inner surface offlexible section 92 includes a tapered surface 96 adapted for engagementwith tapered surface 56 of button assembly 32 and a complimentarytapered surface 98. Surfaces 96 and define the inner surface of finger94.

Proximal portion 78 of dial assembly 34 further includes a firstU-shaped groove 100 (FIG. 3) and a second U-shaped groove (not shown)which form flexible legs 102, 104. Referring to FIG. 10, each leg 102,104, includes an inwardly extending finger 106, 108, and an outwardlyextending finger 110, 112, distal to the inwardly extending finger.Inwardly extending finger 106 includes proximal tapered surface 114,flat 116, and distal tapered surface 118. Likewise, finger 108 includesproximal tapered surface 120, flat 122, and distal tapered surface 124.Outwardly extending finger 110 comprises a proximal tapered surface 126,a flat 128, shoulder 130, enlarged diameter surface 132, and distaltapered surface 134. Outwardly extending finger 112 includes a proximaltapered surface 136, a shoulder 138, an enlarged diameter surface 140,and a distal tapered surface 142.

Referring to FIG. 3, a series of axial splines 143 are arrangedcircumferentially about the inner surface of dial assembly 34 at thearea where proximal portion 78 meets intermediate portion 80. Thecircumferential array of splines 143 is interrupted by legs 102 and 104.In one embodiment, there are ten splines 143 positioned about the innercircumference of dial assembly 34. Referring to FIGS. 3 and 10, there isshown a plurality of splines 144 extending circumferentially about theproximal interior surface of intermediate portion 80 of dial assembly34. Unlike splines 143, splines 144 extend 360° about the innercircumference of intermediate portion 80. In one embodiment, eighteensplines 144 are positioned such that each spline is 20 circumferentialdegrees apart from an adjacent spline.

As best shown in FIGS. 7-9, distal portion 82 of dial assembly 34comprises a proximal flange 146, a reduced diameter portion 148, and adistal end comprising a series of elongated splines 150 extendingexternally about the circumference of distal portion 82. Splines 150 arein alignment with splines 144. Therefore, in one embodiment, there areeighteen splines 150, each corresponding to a respective spline 144. Asshown in FIGS. 8 and 9, two of the splines 150 extend axially intoreduced diameter portion 148. These extensions are indicated as splines152.

Referring to FIG. 10, housing parts 24 and 26 form a proximal groove 154having a tapered surface 156. Housing parts 24 and 26 further form ahelical spiral groove 158 and a tapered circumferential surface 160 asshown in FIG. 10. Housing part 24 further includes a semicircular ridge164 near the distal end thereof. Two grooves are formed at the distalportion of housing part 24 to define a flexible finger 166. Housing part26 includes grooves formed therein to define a flexible leg 168 havingan inwardly extending finger 170 at the end thereof. Finger 170 includesa proximal tapered surface 172 which terminates in a flat 174 and avertical edge 176. Housing parts 24 and 26 include transverse ledges178, 180, respectively, to reduce the diameter through the proximal endof the housing. Ledges 178 and 180 include flexible tangs 182, 184,respectively.

As best shown in FIGS. 11-13 and 17, medical delivery device 20 furtherincludes nut 36 and drive stem 38. Nut 36 is generally cylindrical inshape and includes a pair of axially extending grooves 186 (FIG. 2) toform resilient proximal legs 188. Each leg 188 includes a proximalraised portion 190 and two small axially extending splines 192. Thedistal end of nut 36 comprises an enlarged gear-like member 194 having aplurality of teeth 196 thereon. The interior surface of the distal endof nut 36 includes a helical thread 198. Thread 198 extends about 350°about the inner surface of nut 36. A groove 200 is formed at the distalend of drive stem 38 to form legs 226, 228 (FIG. 2). Ratchet teeth 204are located on two opposing sides of drive stem 38 and axially extendalong the length of drive stem 38 from groove 200 to the distal end,which constitutes plunger engagement portion 206. Helical threads 208extend along the axial length of drive stem 38 legs 226, 228. Drive stem38 fits within the cylindrical opening of nut 36.

As shown in FIGS. 11-14, plunger engagement portion 206 of drive stem 38is in engagement with piston 210 of cartridge 40. Cartridge 40 is housedwithin cartridge retainer 42, which is permanently secured to housingparts 24 and 26. Cartridge 40 is manufactured of glass and comprises atube defining an inner chamber 212 which openly terminates at its distalend in a neck 214 having a cap 216 including a rubber disc 218 disposedthereover. Needle assembly 44 comprises an internally threaded base 220and a delivery needle 222. Internally threaded base 220 is threaded ontoexternally threaded distal portion 224 of body 42. Needle cap 46 fitsover needle 222 to prevent an inadvertent insertion of needle 222 intothe patient. Cap 28 snaps onto cartridge body 42 to complete thepen-like mechanism.

In order to set a dose for injection, it is first necessary to manuallyzero the dial from the initial radial position of the dial resultingfrom the previous injection. The initial radial position of dialassembly 34 with respect to housing part 26 is shown in FIG. 8.Specifically, finger 170 of housing part 26 is located in groove 148 ofdial assembly 34. Groove 148 can be rotated by rotating dial assembly 34with respect to the housing. Dial assembly 34 cannot be axiallyretracted due to the interference between vertical edge 176 of housingfinger 170 and ledge 149 of dial assembly 34. Likewise, dial assembly 34cannot be forced axially forwardly due to the interference betweensurface 89 on ring 91 and end surfaces 33, 35 (FIG. 4) of housing parts24, 26, respectively. If the user mistakenly believes that it isnecessary to depress button assembly 32 to pull out the dial, finger 94falls into groove 154 (FIG. 10), thereby creating an interference thatprevents the dial from being pulled out. Upon continued rotation of dialassembly 34 with respect to housing 26, splines 152 are moved intoengagement with finger 170, as shown in FIG. 7. This is the zero doseradial position of dial assembly 34. This zero dose position iscommunicated to a user in four ways. The user hears a click as splines152 engage finger 170. The movement of finger 170 over the first spline152 into the V-shaped recess 155 between splines 152 causes a vibrationin device 20 that can be felt by the user. In addition, protrusion 88 ondial assembly 34 is in axial alignment with protrusion 153 of housingpart 24, thereby providing a visual indication that the zero doseposition has been reached. This is further visually communicated by thepresence of a symbol in lens 25.

A series of numerals (not shown) are printed on the surface ofintermediate portion 80 of dial assembly 34. These numerals arehelically spaced about the circumference of portion 80 and may numberfrom 1 to 60, in single increments, to indicate a desired dosage. Thelens 25 in housing part 24 is aligned with the numbers so that theappropriate number appears in the lens upon dialing up the dosage. Araised rectangular portion lens 162 (FIG. 10) of lens 25 is located atthe base of lens 25 to enhance the numerals thus making them easier toread.

In its zero dose position, dial assembly 34 may be axially retracted apredetermined distance, e.g. 3 to 5 mm, as illustrated in FIG. 12. Asdial assembly 34 is retracted, ledge 149 is moved past housing finger170 resulting in housing finger 170 being in engagement with splines150. In addition, splines 144 of dial assembly 34 are moved intoengagement with splines 192 of nut 36, as shown in FIG. 12. Whenengaged, rotation of dial assembly 34 causes corresponding rotation ofnut 36. Rotation of drive stem 38 is prevented by a key-keyway type ofengagement between the anti-backup tangs 182 and 184 and drive stem 38.As shown in FIG. 6, tangs 182, 184 form a key, and drive stem 38 forms akeyway which comes into contact with the sides of the key.

Upon rotation of dial assembly 34, fingers 110, 112 move within housinggroove 158 in the proximal direction to retract dial 34, therebyincreasing the axial distance between stop surface 89 of ring 91 andstop surfaces 33, 35 of housing parts 24, 26. Rotation of dial assembly34 causes rotation of nut 36 so that internal helical raised groove 198of nut 36 rotates along external threads 208 of drive stem 38 to causenut 36 to axially retract a corresponding axial distance. As shown inFIG. 9, rotation of dial assembly 34 causes splines 150 to move pasthousing finger 170. The rotation of each spline 150 past finger 170constitutes a single unit of dosage. As each spline 150 moves pastfinger 170, it causes a "click" to occur, thereby providing an audibleindication of each unit of dosage dialed up. In addition, a singlenumeral appears in lens 25 after each unit rotation indicating thecurrent dose selected. Once a dosage has been selected, that dosage maybe made larger or smaller by rotating the dial assembly in either theclockwise or counterclockwise direction.

In one embodiment, dial assembly 34 includes eighteen splines 150 spaced20° apart from one another. It is desired to limit the amount of dosagethat can be dialed to prevent the entire contents of cartridge 40 to bedelivered at once. For example, it may be desirable to limit a measureddosage to a maximum of 60 units. If the dial assembly includes eighteensplines, this would mean that a user could rotate the dial assembly fornearly 31/2 rotations. As shown in FIGS. 12 and 13, as a dosage is beingset, outwardly extending fingers 110 and 112 of dial assembly 34 ride inhelical groove 158 of housing parts 24 and 26. Once a predeterminedmaximum dosage has been dialed up, e.g. 60 units, fingers 110 and 112have reached the proximal end of the helical groove 158. Dial assembly34 cannot be additionally rotated to further increase this maximumdosage due to an interference ledge at the end of helical groove 158.Button assembly 32 prevents the dial assembly 34 from beinginadvertently pushed forwardly during the dosing process due to theinterference between fingers 110, 112 of dial assembly 34, buttonsurface 52, and helical spiral groove 158 in housing parts 24, 26, asshown in FIG. 4. Fingers 110, 112 must be moved out of groove 158 beforethe dial may be moved axially forwardly. Fingers 110, 112 can be movedout of engagement with groove 158 only after fully depressing buttonassembly 32, thereby moving distal button surface 52 out of engagementwith fingers 110, 112.

Once a desired dosage has been set, cap 28 is removed and needle cover46 is removed to expose needle 222. The needle is inserted into thepatient, and recessed surface 70 of button assembly 32 is pushed. FIGS.14-16 illustrate the initial stages of the injection process. Referringto FIG. 14, as button surface 70 is pushed, button assembly 32 movesforwardly independently of dial 34 until button distal surface 52bottoms out against internal dial shoulder 141. Thereafter, button 32and dial 34 are moved together. Referring to FIG. 15, as dial 34 beginsto move forwardly, tapered finger surfaces 134, 142 are forced out oftheir respective threads 158. This causes fingers 110, 112 to flexradially inwardly. As button 32 is further pressed, fingers 110, 112move out of respective threads 158, as shown in FIG. 16. As button 32continues to be pressed, fingers 110, 112 move into and out of theremaining threads 158 in a like manner until dial 34 reaches its end ofdose position shown in FIGS. 10 and 17. The movement of edge 95 (FIG. 4)of dial finger 94 past housing edge 157 (FIG. 4) and into groove 154(FIG. 10) creates an audible "click" sound, thereby providing an audibleconfirmation that the entire dosage has been injected. Finger 94 is inclose proximity to stop surfaces 89 and 33, 35.

As dial 34 is initially moved forwardly, splines 144 move out ofengagement with splines 192 of nut 36 to decouple dial 34 from nut 36prior to any axial movement of nut 36. Dial 34 moves axially withrespect to nut 36 until the distal end 193 (FIG. 13) of dial 34 engagesnut flange 194 and moves nut 36 and drive stem 38 forwardly to deliverthe set dosage of fluid.

Referring to FIGS. 10 and 17, forward movement of dial assembly 34 andnut 36 is limited by the engagement of surface 89 of ring 91 withproximal end surfaces 33, 35 of housing parts 24, 26, respectively, asshown in FIG. 14. Referring to FIG. 14, there is a small clearance, e.g.0.4 millimeters, between nut gear or flange 194 and internal ledges 178,180 of housing parts 24, 26, respectively. In another embodiment, theend-of-dose stop may be designed to occur between nut flange 194 andledges 178, 180.

Movement of drive stem 38 is prevented in the proximal direction due toanti-backup tangs 182, 184 being in engagement with ratchet teeth 204.This assures that head 206 of drive stem 38 remains at all times inconstant engagement with piston 210.

Once a dosage has been completed, the user releases his finger fromrecessed button surface 70. Upon releasing pressure from surface 70, theflexible fingers or springs 62, 64 return from their stressed conditionsback to their relaxed conditions, thereby automatically retracting thebutton assembly 32 back to the automatic lockout position shown in FIG.11 to prevent the dial assembly 34 from being inadvertently advancedwhen it is again moved to its retracted position.

Medication device 20 further includes a mechanism to indicate to theuser that there is an insufficient dosage of medication 212 remaining incartridge 40. Referring to FIGS. 5 and 6, drive stem 38 comprises twolegs 226 and 228. Leg 226 may be of a greater thickness than leg 228.Leg 226 includes an axially extending raised ledge 230 at the end ofexternal thread 208. Leg 228 contains the end 232 of external thread208. The internal helical thread 198 of nut 36 defines a stop surface234 due to the fact that thread 198 extends less than 360* incircumference. As shown in FIG. 17, nut 36 moves toward legs 226, 228 ofdrive stem 38 as drive stem 38 moves within cartridge 40. Once nut 36has axially moved entirely along thread 208 of drive stem 38, stop 234approaches axial ledge 230, as shown in FIG. 5. Additional rotation ofnut 36 results in stop 234 engaging ledge 230, as shown in FIG. 6. Thisprevents the user from dialing up a higher dosage. Nut 36 may be rotatedback in the opposite direction to reduce the dosage if desired. Thisrotational stop mechanism provides a very accurate indication to theuser of the dosage remaining in the cartridge.

It will be appreciated that the foregoing is presented by way ofillustration only, and not by way of any limitation, and that variousalternatives and modifications may be made to the illustrated embodimentwithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A method of delivering a selected dosage ofinjectable product wherein a container of the injectable product ispositioned in a housing of a medication dispensing device, the containerhaving an exit at a first end and a movable piston sealing the containeropposite the first end, the container being positioned in the housingwhereby a drive stem of the medication dispensing device is engaged withthe piston, the medication dispensing device further including a dialassembly operably engageable with the drive stem and a knob operablyengageable with the dial assembly, the method comprising the stepsof:preventing axial displacement of the knob and dial assembly when theknob and dial assembly are in an initial axial position and not in apredetermined zero setting rotational position; rotating the knob to thepredetermined zero setting rotational position while retaining the knobin said initial axial position; then axially retracting the knob anddial assembly from the initial axial position without rotation while theknob is in the predetermined zero setting rotational position; thenrotating the knob to set a desired dosage of injectable product to bedelivered; maintaining the drive stem in contact with the piston duringthe steps of axially retracting the knob and dial assembly and rotatingthe knob to set a desired dosage; and manually depressing the knob toforce the set dosage of injectable product to be delivered out of theexit of the container.
 2. A method of delivering a selected dosage ofinjectable product wherein a container of the injectable product ispositioned in a housing of a medication dispensing device, the containerhaving an exit at a first end and a movable piston sealing the containeropposite the first end, the container being positioned in the housingwhereby a drive stem of the medication dispensing device is engaged withthe piston, the medication dispensing device further including a dialassembly operably engageable with the drive stem and a knob operablyengageable with the dial assembly, the method comprising the stepsof:rotating the knob to a predetermined rotational position; axiallyretracting the knob and dial assembly without rotation while in thepredetermined rotational position and actuating a locking mechanism bysaid axial retraction of the knob and dial assembly away from thecontainer, said locking mechanism preventing the dial assembly frombeing non-rotationally axially translated towards the container; thenrotating the knob to set a desired dosage of injectable product to bedelivered; maintaining the drive stem in contact with the piston duringthe steps of axially retracting the knob and dial assembly and rotatingthe knob to set a desired dosage; and then unlocking said lockingmechanism after the step of rotating the knob to set a desired dosage tothereby enable the knob and dial assembly to be non-rotationallymanually advanced to force the set dosage of injectable product to bedelivered out of the exit of the container.
 3. A method of delivering aselected dosage of injectable product wherein a container of theinjectable product is positioned in a medication dispensing device, thecontainer having an exit at a first end and a movable piston sealing thecontainer opposite the first end, the container being positioned in themedication dispensing device whereby a drive stem of the medicationdispensing device is engaged with the piston, the drive stem having anut threadingly disposed thereon, the medication dispensing devicefurther including a dial assembly axially and rotationally movablerelative to the housing, the method comprising the steps of:axiallydisplacing the dial assembly relative to the nut without rotation of thedial assembly to thereby engage the dial assembly with the nut so thatthe dial assembly and nut can thereafter rotate in unison; then settinga desired dosage of injectable product to be delivered by rotating thedial assembly which in turn rotates the engaged nut thereby axiallyrepositioning the nut on the drive stem; maintaining the drive stem incontact with the piston and preventing relative rotation of the drivestem and the housing during the steps of axially displacing the dialassembly and setting a desired dosage; and manually advancing the nuttowards the container to force the set dosage of injectable product tobe delivered out of the exit of the container.